This invention relates to measurement of the length and the characteristic impedance at any point on the measured length of any wire medium, The invention is suited to the measurement of any wire medium, including coaxial cable or two-wire twisted pair telephone lines in the environment of a local area network used for digital communication. More particularly, this invention relates to the measurement of the pulse characteristic impedance of a medium for signals in a bandwidth in a range to microwave frequencies.
One of the challenges of office communications is to be able to communicate data signals through wire media without signal reflections. What is therefore needed is an apparatus which provides accurate and low-cost signal measurement.
Prior proposed solutions to the problem of measuring impedance have involved the use of a time domain reflectometer comprising a pulse generator and an analog oscilloscope combined in a unit suitable for use outside of a laboratory. Examples are the Tektronix Models 1502 and 1503 TDR cable testers. In order to properly utilize such an instrument, the operator must be sufficiently skilled and trained to operate the various controls and interpret the display of reflected signals on the screen of the internal oscilloscope.
The time domain reflectometry technique is old and well-known. The technique involves introducing a pulse excitation at a measurement point and observing the amplitude of the reflection over a range of time delays.